Added support for custom object formatters

Custom object formatters allow users to customize how an object is
stringified in matcher failure messages. This can already be done by
adding a `jasmineToString` method to the objects in question. But
it's not always desirable or possible to do that, particularly when
objects of a given "type" do not inherit from a specific prototype.
For instance, suppose a web service returns a list of foos that are
deserialized from JSON, e.g.:

   { fooId: 42, /* more properties */ }

The only way to define `jasmineToString` on those is by writing code to
add it to each instance at runtime. But a custom object formatter can
recognize that the object it's looking at is a foo and format it
accordingly:

   jasmine.addCustomObjectFormatter(function(obj) {
      if (typeof obj.fooId !== 'number') {
            return undefined;
        }

        return '[Foo with ID ' + obj.fooId + ']';
    });

Unlike `jasmineToString`, custom object formatters are scoped to a
particular spec or suite and don't require any changes to the code
under test.

spec/core/EnvSpec.js

@@ -305,8 +305,9 @@ describe('Env', function() {
     });
   });
 
-  it('creates an expectationFactory that uses the current custom equality testers', function(done) {
+  it('creates an expectationFactory that uses the current custom equality testers and object formatters', function(done) {
     function customEqualityTester() {}
+    function customObjectFormatter() {}
     function prettyPrinter() {}
     var RealSpec = jasmineUnderTest.Spec,
       specInstance,
@@ -321,11 +322,15 @@ describe('Env', function() {
 
     env.it('spec', function() {
       env.addCustomEqualityTester(customEqualityTester);
+      env.addCustomObjectFormatter(customObjectFormatter);
       expectationFactory('actual', specInstance);
     });
 
     env.addReporter({
       jasmineDone: function() {
+        expect(jasmineUnderTest.makePrettyPrinter).toHaveBeenCalledWith([
+          customObjectFormatter
+        ]);
         expect(jasmineUnderTest.MatchersUtil).toHaveBeenCalledWith({
           customTesters: [customEqualityTester],
           pp: prettyPrinter
@@ -337,8 +342,9 @@ describe('Env', function() {
     env.execute();
   });
 
-  it('creates an asyncExpectationFactory that uses the current custom equality testers', function(done) {
+  it('creates an asyncExpectationFactory that uses the current custom equality testers and object formatters', function(done) {
     function customEqualityTester() {}
+    function customObjectFormatter() {}
     function prettyPrinter() {}
     var RealSpec = jasmineUnderTest.Spec,
       specInstance,
@@ -353,11 +359,15 @@ describe('Env', function() {
 
     env.it('spec', function() {
       env.addCustomEqualityTester(customEqualityTester);
+      env.addCustomObjectFormatter(customObjectFormatter);
       asyncExpectationFactory('actual', specInstance);
     });
 
     env.addReporter({
       jasmineDone: function() {
+        expect(jasmineUnderTest.makePrettyPrinter).toHaveBeenCalledWith([
+          customObjectFormatter
+        ]);
         expect(jasmineUnderTest.MatchersUtil).toHaveBeenCalledWith({
           customTesters: [customEqualityTester],
           pp: prettyPrinter